Y- Chromosome Markers Applications In Sexual Assault Cases

Background

In mammals generally, the Y- chromosome is inherited via the sperm cell and because it is peculiar to the male sex, it is known as the sex determining part of the sex chromosomes (Peter, 2012). Establishing the sex of the obtained biological material from a crime scene can be of great value in the examination and verification of such cases (Alshamali et al. , 2004). Male DNA can be specifically identified by targeting the repetitive elements within the Y-chromosome which is not present in females (Jobling et al. , 1997). Therefore, the existence of Y chromosome is used in the identification of human gender by indicating the formation and development of the testis. This particular role of the chromosome accounts for some of its unique features, thereby attracting researchers who are interested in knowing more about the genetic history of human (Jobling et al. , 1997). Most of the violent crimes are traced to male (Wrigley-Asante, 2016). Study in the recent times has proved that about 93 % of violence crimes were against the victim and 99 % of sexual offences reported in Wales and England were committed by male. Thus, biological samples of the perpetrator which is recovered from the crime scene would be an informative tool in identifying the culprit when Y-chromosome specific markers are employed (Jobling et al. , 1997).

Y-STR Applications In Sexual Assault

In forensic science, studies have proved the application of Y-chromosome short tandem repeats (Y STRs) typing in detecting the identity of male, especially in solving cases related to paternal origin (Example of this situation is the case that linked Emmings Jefferson whose mother served as a slave to the one time America president Thomas Jefferson to his putative father Thomas Jefferson), identifying disaster victims, genealogical search as well as detection of male culprit in crime cases like sexual assaults (Alshamali et al. , 2004; Kayser, 2017; Khana et al. , 2017; Roewer, 2009). Objectively, in sexual assault cases, Y-STR is not to replace the existing markers but contribute to overcoming some of their limitations (Roewer, 2009). For instance Y-STRs have found applications in cases such as; (a) Recovering admixture of stains (in vaginal swabs) suspected to have a higher DNA component of the female victim than that of the male perpetrator. This is because amplification of female DNA will be impossible with well designed Y STR markers in such a mixture (b) When sperm tests in alleged sexual assaults gives a non convincing or negative result (c) Where the alleles of the likely male is not up to the threshold identification for autosomal loci (d) Where the semen stains are old or when the degradation of most of the spermatozoa are presumed and differential extraction has failed (e) where screening of huge amount of semen or related stains are required as well as where the sperm donors in a stain is suspected to be more than one male, Y chromosome markers can help to determine the numbers of culprit provided that they are not related to one another (f) where determining the paternal relatives of a stain donor becomes necessary, This was one of the approaches employed in solving the cold case of Vaastra Marianne of Friesland in Netherland (Hanson and Ballantyne, 2007; Keyser Keyser, 2017; Krenke et al. , 2003; Roewer, 2009). The effectiveness of this typing system has been attributed to the lack of consistency of the Y-loci among human population and the possibility of simultaneously typing a multiple Y-STRs in one PCR reaction. Similarly, as a result its haploidy and non recombining property, differences in the sequence of the Y chromosome can be attributed to the aggregation of de novo mutations (Ali and Hasnain, 2002).

Merits And Weaknesses Of Y-STR Typing In Casework

As a result of its one-parent mode of inheritance and the non-recombining features of the Y-chromosome markers are responsible for it having an edge over other available markers in forensic cases related to human identification, although these qualities have also limited its usage in some cases (Kayser, 2007; keyser, 2017). One of the major merits of Y-chromosome markers is the ability to overcome the difficulty of preferential amplification, allowing for the identification of the male components in a DNA admixtures and this means that the Y-chromosome has a higher male specificity (Kayser, 2007; Krenke et al. , 2003). Y-STRs could be the only available option when a case requires the tracing of the male ancestors of a perpetrator. In addition, the interpretation of Y-STRs profiling result is not difficult since they combine to form a single peak haploid. In this regard, the efficiency of the Y-STR markers and different commercial kits of about 17 markers including the Y-filer developed in the recent times were all proved to be encouraging with different reported cases in different populations (Ballantyne et al. , 2012). Considerable and improved databases (for instance http: //usystrdatabase. org) have now been developed ad applied in the estimation of the frequency of the Y-STR haplotype among the worldwide scattered population of human being (Ballantyne et al. , 2012). Even though, the diversity of the Y-filer haplotypes is good for identifying a non-closely related family, discrimination from person to person is substantially lesser in comparison with that of the autosomal STRs.

This means it lacks the ability to indicate the exclusion of patri-lineal relations of a suspect (Keyser, 2017). (Ballantyne et al. , 2012; Mulero, 2006). This drawback can be attributed to the low mutation rate of the marker and this account for the reason why Y-chromosome profiles are not obtained in criminal database. Generally, the specific Y-STRs used in forensic science also account for the restriction in the resolution of haplotype (Ballantyne et al. , 2012). For instance, the initial discovery of the 9 Y-STRs indicating the minimal haplotype occurred at a time when very few Y-STRs were identified from a limited population data, thus giving lower power of resolution when compared to other subsequent markers that were developed (Kayser et al. , 1997). In addition, the available Y-STRs in the contemporary times only provide a narrow resolution for historical or cultural populations (like the patri-local residence) which have experienced prompt enlargement (Alghafri et al. , 2015; Kayser, 2017). This can be due to the complete reduction in their Y-chromosome diversity. Studies have shown that the Y-STR haplotype diversity, as studied using the currently available Y-STR markers can be improved for male lineage distinction via additional Y-STRs (Ballantyne et al. , 2012). THE UniQ Typer™ Y-10 SYSTEM. The typing system known as UniQ Typer™ Y-10 was generated with the modification of the chemistry from the normal appearance to overcome the limitation of Y-STRs (D’Amato and Kasu, 2017). This multi-copy marker is made up of only four rapidly mutating markers which are DYS449, DYS612, DYS518 and DYS626. Other markers found on the kit are DYS447, DYS481, DYS504, DYS644, DYS710 and DYS385 (D’Amato and Kasu, 2017). The efficiency of the kit was tested on three indigenous populations of South Africa and compared with those of the other available commercial kits (D’Amato et al, 2011). The results from this comparison proved that the former (UniQ-Typer™ Y-10) has a higher potential for discrimination (D’Amato et al, 2011).

Sexual Assaults In Ghana

Often cases reported of sexual assault against female adolescents and adults all over the world are on the rise as compared to sexual offences against males (Kaur et al. , 2017). Sexual assault cases in Ghana are endemic. For instance about 40,000 cases were recorded between the years 2015 and 2016 (Quarshie et al. , 2018). The victims spanning from girls below 10-year old to women of about 60-year old, identified ladies of middle age (18 to 30 years) to be more victimized in comparison to other age groups (Quarshie et al. , 2018). Due to the inability of victims to point out their rapist and the available but controversial method of examinations, probably this figure may be larger than presently observed in few years time. Therefore, at this point it becomes crucial for a more specific and sensitive techniques to be developed for the identification of perpetrators (Quarshie et al. , 2018). Currently Ghana comprises of ten regions with sixty diverse ethnic groups, fifty two languages and about hundred dialects (Ghana Web, 2012). Regardless of it rich diversity, movement of individual have spread people from different ethnic groups across the country without breaking the bond of ethnicity. The diversity of the Y chromosome is dependent on some conditions like size of the population (genetic relationship which is always higher in rural settings compared to urban), male’s way of life or behaviour, marriage styles as well as migration history (Ali and Hasnain, 2002).